The present invention relates to a tape cassette for short-time recording, suitable for use in a device such as a video tape recorder, in which signals are recorded in and reproduced from a recording tape wound over a predetermined portion of a circumference of a tape guide drum incorporating a transducer.
Video tape recorders (referred to as "VTR", hereinunder) have spread remarkably. In order to use portable VTRs for the purpose of outdoor recording and playback, reduction in size and weight is an important subject for the comfort of the user who handles the portable VTR outdoors. Without doubt, the tendency of the reduction in size and weight of video cameras and electric circuits will be further enhanced owing to the current effort for the reduction in the size of parts and to wide use of semiconductor parts.
On the other hand, the size of the mechanism of VTR is limited by the size of a tape cassette and the diameter of a tape guide drum. Practically, however, the effort for the reduction in the size of the VTR mechanism encounters a limit due to the size of the tape cassette and the diameter of the tape guide drum. In the modern VTRs, a tape cassette is positioned in the same plane as a tape guide drum at a predetermined distance from the latter, and tape is extracted from the cassette and wound round the tape guide drum by a specific mechanism. The reduction in size is limited also by the design of this mechanism. In order to reduce the size of this mechanism, a short-time recording tape cassette referred to as "VHS-C" has been proposed for VHS type video tape recorders. It has been also proposed to reduce the size of the tape guide drum by adopting so-called 1.5 head type or 4-head type drum, although such a drum is usable only for playback.
Thus, miniaturization of the VTR mechanism has been promoted through efforts to reduct the size of both the tape guide drum and the tape cassette. An explanation will be made hereinunder as to the practical measure for the reduction in the size of the tape cassette.
A tape cassette 202 of VHS-C type (referred to as "C-cassette", hereinunder) has a reel axis distance and a tape stretching position which are different from those of a standard long-playing tape cassette of VHS type (referred to as "standard tape cassette", hereinunder) as shown in FIG. 38. In order to provide interchangeability between the C-cassette and the standard tape cassette, it is a known measure to mount the C-cassette on an adapter cassette 201 having a maximum external size equal to that of the standard tape cassette. By using this adapter cassette, the reel axis distance and the tape running position which are the same as those of the standard tape cassette are obtained to make the C-cassette adaptable to the VTR designed for use in combination with the standard tape cassette. Needless to say, it is impossible to mount the standard tape cassette on a VTR designed for C-cassettes. The principal advantage of the adapter cassette type system represented by the VHS-C system resides in the miniaturization of the mechanism mentioned before. This system, however, involves the following problems or shortcomings.
(1) An expensive adapter cassette 201 is required for the mounting of the C-cassette on the VTR designed for the standard tape cassette. The user is obliged to purchase this expensive adapter cassette and to take a trouble of mounting the C-cassette into and out of the adapter cassette.
(2) For extracting the tape from the C-cassette 202 mounted on the adapter cassette 201 to the same position as that of the standard tape cassette, the front cover of the C-cassette in the adapter cassette 201 has to be kept opened. The front cover in the opening position is not allowed to project forwardly beyond the front edge of the adapter cassette 201. These requirements seriously limit the construction of the front cover of the C-cassette 202. In fact, existing C-cassettes are devoid of any sealing structure for sealing the tape and have no mechanism for locking the front covers.
(3) In the C-cassettes, the position of a feed reel 203 corresponds with the position of a feed reel in the standard tape cassette, in order to give a preference to the tension characteristics. A take-up reel 204 is constituted by a shaft provided in the C-cassette 202, such that it is driven through intermediate gears 205,206 in the adapter cassette 201. With this arrangement, under the influence of fluctuation in the meshing conditions of the gears 205 and 206, displays can be distorted and undesirable effects such as wow and flutter are produced.
Another proposal for miniaturization of the portable VTR employs a small-sized cassette without the use of the adapter cassette which causes all the problems mentioned above. This small-sized cassette is a 3/4 inch cassette shown in FIG. 39, already used in broadcasting stations. A small-sized cassette 207 in question has the same reel-axis distance and tape running position as those of the standard tape cassettes 208. In this case, however, the diameter of a reel flange 209 is reduced by an amount corresponding to a short period of recording time, so that the width W of the cassette, as well as the distance D between the reel shaft and the rear surface of the cassette, is reduced to permit miniaturization of the cassette. This proposal, however, has the following shortcomings, although it can overcome the disadvantages of the adapter cassette type system mentioned before.
(1) For allowing two types of cassettes of different external sizes to be inserted in a VTR, the cassettes are formed at the bottom surfaces thereof with concaved guide recesses shown by broken lines in FIG. 39. This increases the cassette thickness unnecessarily.
(2) The cassette holder of the VTR must be provided with a guide protrubence for matching the guide recess in the cassettes. When the small-sized cassette is inserted into the VTR designed for the standard tape cassette, the cassette has to be inserted deeper into the VTR than in the case of the standard tape cassette 208, because the distance D between the reel shaft and the rear end surface of the cassette is smaller in this cassette than in the standard tape cassette. This considerably impairs the handling characteristics.
(3) With the small-sized cassette 207 inserted deeper into the cassette holder, withdrawal of the cassette is more difficult than insertion thereof. So, the user catches a notch 211 is formed in the center of the rear surface of the small-sized cassette to afford a holder for a finger for withdrawal. This operation is also very troublesome. For allowing a finger to enter the cassette holder and hold the small-sized cassette, there is naturally a limit on the size of the small-sized cassette. Namely, this withdrawing method is not possible unless the cassette has the thickness and size corresponding to the 3/4 inch tape.
(4) Miniaturization of the small-sized tape cassette 207 on the basis of the standard tape cassette has a practical limit because this cassette has the same reel-axis distance and tape running position as the standard tape cassette. This proposal, therefore, is not so effective as the VHS-C system in the miniaturization of the mechanism.
These two proposals for the miniaturization of cassette, however, have respective merits and demerits, and are still unsatisfactory.